Circuit Description
The DTC P0505 Idle Control System diagnostic observes engine speed in order to monitor the operation of the IAC valve. The powertrain control module (PCM) controls engine idle speed with the idle air control valve. To increase the idle speed, the PCM pulse width modulates the OPEN solenoid within the IAC valve. This action turns a cylinder within the IAC valve, allowing air to bypass the throttle plate. The PCM regulates fast idle speed via the IAC valve by increasing the opening of the air bypass port. The PCM regulates slow idle speed via the IAC valve by decreasing the opening of the air bypass port.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0505 Idle Control System
Conditions for Running the DTC
| • | DTC P0011, P0012, P0031, P0032, P0100, P0101, P0102, P0103, P0115, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0130, P0133, P0134, P0171, P0172, P0300, P0301-P0304, P0335, P0340, P0341, P0351-P0354, P0385, P0500 are not set. |
| • | The battery voltage is more than 11 volts. |
| • | The engine coolant temperature is at least 75°C (167°F). |
| • | The engine is running at idle conditions. |
| • | Vehicle speed is less than 3 km/h (1.8 mph). |
| • | When the above conditions have been met, DTC P0505 runs once per drive cycle for Condition 1 and Condition 2. |
| • | When the above conditions have been met, DTC P0505 runs continuously for Condition 3. |
Conditions for Setting the DTC
| • | Condition 1--The observed engine speed at idle is less than the expected engine speed by 100 RPM or more. |
| • | Condition 2--The observed engine speed at idle is more than the expected engine speed by 200 RPM or more. |
| Either of the above conditions has occurred 5 times or more this drive cycle. |
| • | Condition 3--The IAC motor duty cycle is less than 10 percent or more than 90 percent for 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with an active Condition 1 or Condition 2 fault. |
| • | The PCM illuminates the MIL immediately with an active Condition 3 fault. |
| • | The PCM stores the conditions which were present when the DTC set as Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present. |
| • | The DTC clears after 40 consecutive warm-up cycles have occurred without a fault. |
| • | A DTC can be cleared by using the scan tool Clear DTC Information function. |
Diagnostic Aids
| • | With the engine idling at a normal operating temperature and all accessories OFF, monitor the following parameters on the scan tool: |
| - | The IAC Motor Command--25 to 45 percent |
| - | Engine speed--750 to 850 RPM |
| - | Electrical load--No |
| - | Commanded A/C--OFF |
| - | If any of the above parameters is outside of the typical value as indicated, inspect for the cause and repair as necessary. |
| • | Inspect the carpet or floor mat for interfering with the free movement of the accelerator pedal. |
| • | The scan tool can be used to isolate the cause of an intermittent DTC P0505. Engine idle speed can be controlled with the scan tool. Operate the IAC valve with the scan tool while checking for a smooth increase and decrease in engine speed. If engine speed can be controlled, the IAC system is functioning normally. |
| • | Check for the following conditions: |
| - | Any blockage of the air intake system |
| - | Any blockage of the IAC passage |
| - | Excessive deposits on the throttle plate or the throttle bore |
| - | Any large vacuum leaks |
| • | An intermittent malfunction may be caused by a fault in the IAC sensor electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions . |
| • | The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set. |
| • | If the DTC P0505 does not reset, but a driveability symptom still exists, refer to Symptoms - Engine Controls . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step simulates the pulse width modulated (PWM) signal supplied to the IAC valve by the PCM by rapidly grounding and un-grounding terminal 1 of the IAC valve.
-
The most likely cause of no power is an open circuit condition between the IAC valve connector terminal 2 and the splice. A shorted or inoperative EFI relay circuit will cause a no-start condition.
Step | Action | Yes | No | ||||
|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | |||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||
2 |
Does this DTC reset? | Go to Step 4 | Go to Step 3 | ||||
3 | Is there an idle quality concern? | Go to Diagnostic Aids | |||||
4 |
Did you find and correct the condition? | Go to Step 13 | Go to Step 5 | ||||
5 |
Does the test lamp illuminate? | Go to Step 6 | Go to Step 9 | ||||
6 | Using a test lamp connected to B+, probe terminal 3 of the IAC valve connector . Does the test lamp illuminate? | Go to Step 7 | Go to Step 10 | ||||
Does engine speed increase as the terminal 1 jumper is rapidly grounded ON and OFF? | Go to Step 8 | Go to Step 11 | |||||
8 |
Was a circuit repair made? | Go to Step 13 | Go to Step 12 | ||||
Is the action complete? | Go to Step 13 | -- | |||||
10 | Repair the open IAC valve ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | Go to Step 13 | -- | ||||
11 |
Important: The IAC valve seals the coolant passage of the throttle body. Replace the IAC valve. Refer to Idle Air Control Valve Replacement . Is the replacement complete? | Go to Step 13 | -- | ||||
12 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Is the replacement complete? | Go to Step 13 | -- | ||||
13 |
Are any DTCs displayed on the scan tool? | Go to Step 14 | Go to Step 2 | ||||
14 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK | ||||
